$ \left(\dfrac{10}{7}\right)^{-3}$
Solution: $= \left(\dfrac{7}{10}\right)^{3}$ $= \left(\dfrac{7}{10}\right)\cdot\left(\dfrac{7}{10}\right)\cdot \left(\dfrac{7}{10}\right)$ $= \dfrac{49}{100}\cdot\left(\dfrac{7}{10}\right)$ $= \dfrac{343}{1000}$